Little Gem Lettuces with Marinated Anchovies and Bottarga

Name: Little Gem Lettuces with Marinated Anchovies and Bottarga
Ingredients: 2 tbsp. white wine vinegar; 4 oil-cured or salt-cured brown anchovy fillets; 2 tbsp. Dijon mustard; 1 small garlic clove, grated or minced; 1 pinch salt; 1 pinch sugar; 2 cups canola oil; 5 heads little gem lettuces (or any petite crunchy lettuce, like baby romaine), trimmed and separated into leaves; Fresh lemon juice, for drizzling; Extra-virgin olive oil, for drizzling; About 10 marinated white anchovies such as boquerones, for garnish (optional); Finely grated bottarga (cured mullet roe), for garnish; Thinly sliced spring onion, for garnish (optional); Freshly ground black pepper